8 & 9. Cable Selection Flashcards
1
Q
Explain the circuit design process
A
- Determine the design current (Ib).
- Select the rating for the protection device (In).
- Calculate the cable rating (Iz).
- Select a cable size from BS 7671 which will carry the current rating (It).
- Make sure to pick the correct installation method. - Calculate Voltage Drop (Vd)
- Check for Shock Risk constraints.
- Check for Thermal Constraints
2
Q
What is the allowable volt drop?
A
3% for lighting circuits
5% for LV power circuits
3
Q
When checking for thermal constraints, what is K?
A
70 Degrees: 115
90 Degrees: 143
4
Q
What is the Maximum Ze for:
A TN-S Earthing System
A TN-C-S Earthing System
A
TN-S: 0.8 Ohms
TN-C-S: 0.35 Ohms